The present disclosure relates to a gas turbine engine and, more particularly, to a geared architecture therefor.
Epicyclic gear systems with planetary or star gearboxes may be used in gas turbine engines for their compact designs and efficient high gear reduction capabilities. Planetary and star gearboxes generally include three gear train elements: a central sun gear, an outer ring gear with internal gear teeth, and a plurality of planet gears supported by a planet carrier between and in meshed engagement with both the sun gear and the ring gear. The gear train elements share a common longitudinal central axis, about which at least two rotate.
In gas turbine engine architectures where speed reduction transmission is required, the central sun gear generally receives rotary input from the powerplant, the outer ring gear is stationary and the planet gear carrier rotates in the same direction as the sun gear to provide torque output at a reduced rotational speed. In star gear trains, the planet carrier is held stationary and the output shaft is driven by the ring gear in a direction opposite that of the sun gear.
During flight, lightweight structural engine case assemblies may deflect upon aero and maneuver loads that may cause transverse deflection commonly known as backbone bending. This deflection may cause the individual sun or planet gear's axis of rotation to lose parallelism with the central axis and may result in some misalignment at gear train journal bearings and at the gear teeth mesh. This misalignment may lead to efficiency losses and the potential for reduced life.